Fix npm install in Dockerfile to only install production packages

Dockerfile

@@ -10,11 +10,11 @@ COPY . .
 # Change directory to src/server/
 WORKDIR /usr/src/isleward/src/server/
 
-# Install npm modules specified in package.json
-RUN npm install --only-production
+# Install only production npm modules specified in package.json
+RUN npm install --only=production
 
 # Expose container's port 4000
 EXPOSE 4000
 
 # Launch Isleward server
-CMD ["node", "index.js"]
+CMD ["node", "index.js"]